Competitors have covered thousands of kilometers since the World Solar Challenge kicked off on Sunday, but in a way not much has changed since then. Defending champions Nuon remain in the lead heading into the final day of racing, as adverse conditions appear to be doing the rest of the solar-powered field no favors.

Competing in the Challenger Class, Holland's Nuon Solar Team rolled into camp at the end of day three with a massive 56-minute lead over the second placed University of Michigan Solar Team. As the clouds continued to cast a shadow over racers on day four, Nuon stretched this lead out to 59 minutes with an average speed of 81.5 km/h (50 mph), around 5 km/h (3 mph) faster than its closest rival.

This lead appears to be pretty much unassailable heading into the last day of racing, but then again, it is solar-powered racing across the Australian Outback, so conceivably anything could happen.

Over in the Cruiser Class, meanwhile, where competitors are awarded points based on their energy efficiency and payloads, Team Eindhovern has maintained its commanding lead with an efficiency score of 80. The next best is Germany's Bochum SolarCar Team with 27.4.

The Challenger Class is expected to roll across the finish line in Adelaide on Thursday afternoon local time, while the Cruiser Class is expected some time on Friday. Stay tuned to New Atlas for a full wrap-up.